You have asked a complex question.
Archicad models are rendered in several ways, so when you "change the color" of a surface, you must work comprehensively.
The drafting views are easiest because they derive their color from the color set in Archicad's Internal Engine settings. A vector fill overlaid can be viewed in analytical section/elevation views or as Internal rendered 3D views.
Should an underlying texture map be present as a surface in the Internal Engine material definition, it CAN be seen in the OpenGL rendering, too.
I assume that your problem is in the LightWorks Rendering. you've probably changed the material color in the internal engine dialog and not transferred that info to LightWorks.
But in LightWorks, a facility exists to change the color tint of any bitmap/texturemap.
For my example, I'm posting the dialog from an Archicad 11 material that uses an alpha channel image to create the siding shadow illusion. In this case, the image is used only as a depth indicator and the color of the material is determined with the LightWorks Color Shader "plain."
So:
In your case, Use your siding texturemap in the LightWorks material definition by placing the image in both:
Color Class shader "Wrapped Filtered Image" AND
Displacement Class Shader "Wrapped Bump Map."
You will notice that in the "Wrapped Filtered Image" parameters a "Color" parameter appears. Use this setting to change the color of your siding.
Dwight Atkinson